A 10-year-old girl has died of bird flu in Vietnam, the country's 12th confirmed victim in a month.

Medical official Ngo Van Hoang said the girl developed a high fever and bad cough a week after helping her family bury some dead chickens.

The spike in deaths has raised worries the disease, which last year hit 10 Asian countries, could re-emerge.

It has also renewed scientists' fears that the virus could mutate into a form that is easily spread human-to-human.

Vietnamese officials are investigating whether a 13-year-old girl and her mother from Dong Thap province, who both died of the virus in the last two weeks, infected each other, or caught the disease from infected ducks.

They are also concerned about a 25-year-old Cambodian woman who died in southern Vietnam on Saturday from suspected bird flu.

Tests are being done to confirm the cause of her death, but doctors told Reuters news agency that they were worried because her brother recently died of respiratory failure.

H5N1 BIRD FLU VIRUS

Principally an avian disease, first seen in humans in Hong Kong, 1997

Almost all human cases thought to be contracted from birds

Isolated cases of human-to-human transmission in Hong Kong and Vietnam, but none confirmed

The strain of virus causing the deaths - H5N1 - is suspected of jumping from human to human once before, in September last year, when a mother in Thailand probably became infected from her daughter.

But experts are especially worried in case the virus combines with a human flu virus, if someone were to be simultaneously infected with both.

If the viruses then exchanged genes, a new, highly infective virus could be created and be easily passed from person to person.

Holiday risks

In the past months, 12 people have died from bird flu in Vietnam.

The BBC's South East Asia correspondent, Kylie Morris, says it is a particularly difficult time to control its spread.

Many Vietnamese are on the move, returning to their home villages to celebrate Tet - the lunar new year. Chicken is a popular dish for the festival so families are reluctant to slaughter animals which may be sick.

Experts have also warned that colder weather may aid the spread of the disease.

Bird flu has killed 12 people in Thailand and 32 people in Vietnam since January last year.

Tens of millions of chickens and other poultry have already been killed or culled in an attempt to stop the disease spreading.